Create "Theme Options" submenu under Appearance

Description

Right now, core functions that only show up if your theme supports it (background, header, someday maybe more) create a longer list of Appearance submenus. When a user switches themes, they tend to get confused and wonder why the functions are gone. I suggest that we create a new submenu called Theme Options and put those management screens there as tabs, so that it's clear it's theme dependent.

To play devil's advocate to my own suggestion, isn't everything in that section really a theme option, like widgets? Maybe it's not a good idea after all.